The present invention relates to a coating apparatus for coating the surfaces of a series of substrates with coating solution uniformly, and more particularly to a coating apparatus for coating a series of relatively short substrates such as glass plates, aluminum plates, zinc plates or plastic sheets with a coating material such as photo-resist or photographing photosensitive material.
In a conventional method of coating a series of substrates with a coating solution, a flexible, elastic solid curtain member such as a plastic sheet, metal foil, paper or cloth is fastened to the end of a solution supplying unit, and with the end of the solid curtain thus fastened held in contact with the substrate, the coating solution supplied from the solution supplying unit is applied to the substrate (see, for example, Japanese Patent Application Publication No. 16214/1976).
If a multi-layer coating operation is carried out using a solution supplying unit operating according to a method which is adapted to form a plurality of coating solution layers simultaneously, the coating solution layers tend to mix with one another, that is, it is difficult to form coating solution layers uniformly, and the layers on the front end portion of each substrate are thicker than those on the remaining portion (hereinafter referred to as a "steady portion" when applicable).
Moreover, the method is disadvantageous in that there is a tendency for the layer of coating solution formed on the substrate to be not uniform in thickness, namely, the coating solution layer on the front end portion of the substrate is thicker than on the remaining steady portion, and stripes are formed in the layer of coating solution on the remaining steady portion.
FIG. 10 shows a conventional dual layer coating apparatus of the solid curtain type. FIG. 10 shows the coating apparatus in an operating mode in which one substrate 301 has been coated with coating solutions, and the following substrate 310 is next to be coated.
Coating solutions 304 and 314 flowing down a solid curtain 305 form a solution pool 308 along the front edge of the solid curtain 305 while mixing with each other, and drop from the solution pool 308 irregularly. As a result, the coating solution layer formed on the substrate 310 is irregular in thickness; that is, the substrate 310 is coated heavier in its front end portion than in the remaining portion, and in addition the two coating solution layers are mixed on the latter.
FIG. 11 shows another conventional solid curtain type coating apparatus. More specifically, FIG. 11 shows a mode of operation of the coating apparatus in which a substrate 101 has been coated with a coating solution 104, and the next 110 is going to be coated.
The coating solution supplied from a solution supplying unit 103 flows down a solid curtain 105 while forming a solution pool 108 at the front edge of the solid curtain 105, and drops irregularly from the solution pool 108. Hence, in the front end portion of the following substrate 110, the coating solution layer formed thereon is not uniform in thickness in the widthwise direction, and in the remaining steady portion, longitudinal stripes are formed in correspondence to the solution dropping pattern 109.